The present invention relates to a feed rate control device for an electric spark machine, and more particularly to a servo-controlled feed rate control device for precisely controlling the feeding operation of the electrode of a computerized numerical controlled electric spark machine. Under the control of the present invention, the stability of the system is increased, the steady-state error is decreased, and the discharging efficiency is improved.
The well-known technique of electric discharging machining is widely used for removing metallic materials from the surface of a workpiece. In operation, an instantaneous electric spark is continuously supplied between the stationary workpiece to be processed and the electrode of the machine. That is, the machining of the workpiece is completed by controlling the movement of the electrode supplied with a discharging energy with specific frequency to discharge from the electrode to the workpiece. For a useful and perfect electric spark machine, the discharging current strength, the discharging time period, and the movement of the electrode thereof must be controlled precisely and properly in order to keep the discharging spark strength unchangeable and remain the gap between the electrode and the workpiece uniform.
In the operation of the electric discharge machining, the purpose of controlling the feed rate of the electrode is to control that the electrode may move along a predetermined path and keep a narrow gap from the workpiece to be processed to make a continuously discharging performance on the surface of the workpiece. However, it is found that the gap between the electrode and the workpiece is often deposited with undesired carbon deposit and residual metallic materials, which will decrease the discharging efficiency of the system. Besides, the machining parameters of the system and discharging erosion surface occurred on the surface of the electrode also effect the performance efficiency of the system. In this regard, the feed rate of the electrode must be controlled and adjusted according to real operating situations of the system, rather than moved at a constant operation speed.
An ideal discharging voltage of an electric spark machine is shown in FIG. 1. It is preferable that inserting an ignition delay before discharging happening. In this regard, the conventional electric spark machine is designed to be capable of generating a feed rate control signal to servo-motor driving circuit by filtering the signal and comparing the filtered signal with a preliminary reference signal. As shown in FIG. 2, it shows a general function block diagram of a computerized numerical controlled electric spark machine which typically composed of a regulator 10, a CNC interpolator 11, and a driving circuit 12. An electrode 13 is employed, which is capable of performing discharging operation to a workpiece to be processed. The regulator may be used to adjust the stability of the system at the start point of discharging period.
In order to shorten the idle running time, the operator may manually adjust the sensitivity of the system larger, so that the electrode may reach the preliminary discharging position at a faster speed. Further, when the electrode reaches the discharging position, the operator is necessary to adjust the sensitivity lower to make the system stable. It is obvious that the conventional adjusting operation is rather inconvenient in operation.